High expectations for single-wire power exchange

Jean Van Bladel Associate Professor and H.I. Romnes Fellow Daniel Ludois and PhD student Shiying Wang received the award for Best Oral Presentation Paper in Emerging Technology for IEEE Energy Conversion Congress and Exposition (ECCE) 2022. The award was announced at the IEEE ECCE in Nashville, TN in November.

The paper, “A Capacitively-Coupled Single-Wire Earth-Return Power Tether for Aerial Platforms”, asserts that a single-wire earth return (SWER) power transfer is achievable at high frequencies. Says Ludois, “Think of it as making an extension cord that goes to something in the air, but with only a single wire.  Electric circuits need to form a closed loop, so a normal extension cord or transmission line has 2 or more wires. That’s because you need one wire to send current up and another to bring it back down.  Our experiment only needs one wire, which allows for the tether to be a simple bare wire, lightweight, like a kite string, but conducting.” The wire was made from high-strength steel and used at a high voltage similar to the electric grid.

The team tested their theory by carrying the resonator and load 70 meters into the air with a helium filled balloon at the University of Wisconsin–Madison Arlington Agricultural Research Station in Arlington, Wisconsin. According to Ludois, “We send current up through our single wire, and a resonator on the aerial object completes the circuit by capacitively coupling to the surrounding world to return to earth. Ultimately we demonstrated that our proof of concept system was 93% efficient.  Next steps for us to optimize it so it can fit in a drone.”

The draw to this discovery is that the devices could stay in the air longer than is currently possible as they would no longer require batteries or trips back to the ground for charging. Future applications of this research could be for drones, wind turbines, solar panels, or other higher elevation devices. More specifically, the technology could eventually be used for emergency situations such as after an earthquake when lights and cameras are needed to survey areas that may be unsafe for humans to enter.